In electrography, image charge patterns are formed on a support and are developed by treatment with an electrographic developer containing marking particles which are attracted to the charge patterns. These particles are called toner particles or, collectively, toner.
One well-known type of electrostatographic developer comprises a dry mixture of toner particles and carrier particles. Another type comprises toner particles without carrier. The former type of developer is commonly referred to as "two component developer". The latter typer of developer is commonly referred to as single component developer. This terminology can be a misnomer, for example, some two component developers contain additional small particles, which are sometimes referred to as "third component".
Two component developers are employed in cascade and magnetic brush electrostatographic development processes. The toner particles and carrier particles differ triboelectrically, such that during mixing to form the developer, the toner particles acquire a charge of one polarity and the carrier particles acquire a charge of the opposite polarity. The opposite charges cause the toner particles to cling to the carrier particles. During development, the electrostatic forces of the latent image, sometimes in combination with an additional applied field, attract the toner particles. The toner particles are pulled away from the carrier particles and become electrostatically attached, in imagewise relation, to the latent image bearing surface. The resultant toner image can then be fixed, by application of heat or other known methods, depending upon the nature of the toner image and the surface, or can be transferred to another surface and then fixed.
Electrophotography commonly uses very specialized terminology. For convenience, specialized definitions are provided here for a number of terms.
The term "particle size" used herein, or the term "size", or "sized" as employed herein in reference to the term "particles", means the median volume weighted diameter as measured by conventional diameter measuring devices, such as a Coulter Multisizer, sold by Coulter, Inc of Hialeah, Fla. Median volume weighted diameter is the diameter of an equivalent weight spherical particle which represents the median for a sample; that is, half of the volume of the sample is composed of smaller particles, and half of the volume of the sample is composed of larger particles than the median volume weighted diameter.
The term "charge control" refers to a propensity of a toner additive to modify the triboelectric charging properties of the resulting toner.
The term "glass transition temperature" or "T.sub.g " as used herein means the temperature at which a polymer changes from a glassy state to a rubbery state. This temperature (T.sub.g) can be measured by differential thermal analysis as disclosed in "Techniques and Methods of Polymer Evaluation", Vol. 1, Marcel Dekker, Inc., New York, 1966.
A variety of materials have been added to developers for a wide variety of purposes.
U.S. Pat. No. 3,565,805 to Jones et al teaches a developer including tackifying agents, such as siloxane oil, hydrocarbon oil, animal, fish or vegetable oil, glycerol, fatty acid ester of glycol ether or alkylamine having 12-18 carbon alkyl.
U.S. Pat. No. 3,577,345 to Jacknow et al teaches a two component developer including a solid metal salt of a fatty acid and a solid additive which can have the structural formula: ##STR2## in which R is selected from H, Cl, Br, aryl, alkyl having from 1 to 6 carbons; R' and R" are selected from H, aryl having from 1 to 12 carbons and alkyl having from 1 to 12 carbons, for modifying toner melt and viscosity.
Great Britain 1,117,224 teaches the preparation of toners by a method in which surfactant is added during polymerization of binder. The patent states: "Any suitable surfactant of the well-known cationic, anionic and non-ionic types may be employed." A list of examples of surfactants includes aliphatic amines and their derivatives.
U.S. Pat. No. 4,312,933 to Lu teaches high resistivity toners for use in one component magnetic development systems. These toners include a nitrogen containing compound having the structural formula: ##STR3## where R (or one of the R groups in the quaternary ammonium compound) is 8-22 carbon hydrocarbon, R.sup.1 and R.sup.2 are 1-22 carbon hydrocarbons, the remaining R groups in the quaternary ammonium compound are H or 1-22 carbon hydrocarbons, and A is sulfate, borate, chlorate or halogen.
Toner particles of two component developers often include second agents, which, desirably, provide high uniform net electrical charge to toner particles without reducing the adhesion of the toner to paper or other medium. Many types of charge control agents, materials which impart a positive charge to toner particles in a developer, have been used and are described in the published patent literature.
U.S. Pat. No. 5,002,847 to Utsumi et al teaches toners including a positive charge control agent, such as: nigrosine dyes, alkoxylated amines, quaternary ammonium salts, alkylamides, and a variety of other compounds.
U.S. Pat. No. 4,394,430 to Jadwin et al teaches a two component developer including a quaternary ammonium salt of the formula: ##STR4## where R is 12 to 24 carbon alkyl and X is an anion.
U.S. Pat. No. 3,893,935 to Jadwin et al teaches a two component developer including a quaternary ammonium salt of the formula: ##STR5## where R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are 1-7 carbon alkyl and X is an anion.
U.S. Pat. No. 4,298,672 to Lu teaches a two component developer including an alkyl pyridinium compound or its hydrate of the formula: ##STR6## where R is 15-18 carbon hydrocarbon and A is Cl or Br.
U.S. Pat. No. 5,304,449 to Hollenbaugh, Jr., teaches toner and developers containing as charge enhancing components (1) alkyl pyridinium compounds or their hydrates and (2) tetrasubstituted ammonium salts.
In some electrophotographic applications, two component developers are needed which can maintain certain good characteristics, such as conductivity and charge control, during very long term use of the developer, in which the developer is replenished with additional toner many times. It has been determined that many additives do not maintain uniform characteristics during long term use of the developer. This presents a particular problem in very high volume applications.
It is therefore desirable to provide a two component developer and a method for preparing that developer, which developer is useful in high volume use, and which maintains good coductivity/resistivity and charging characteristics.